Washing process with waste water recycling

ABSTRACT

A process for washing fat- or dye-soiled materials involving: (a) providing a fat- or dye-soiled material; (b) providing an aqueous detergent-containing liquor; (c) contacting the fat- or dye-soiled material with the aqueous detergent-containing liquor, thus forming a washed material and wash wastewater; (d) providing a source of rinse water; (e) rinsing the washed material with the rinse water, at least once, thus forming rinsed material and rinse wastewater; (f) collecting both the wash and rinse wastewater; (g) chemically pretreating the collected wash and rinse wastewater by contacting it with a compound selected from the group consisting of a demulsifier, an oxidizing agent and mixtures thereof to form waste particles; (h) mechanically removing the waste particles from the collected wash and rinse wastewater by flotation or sedimentation to form prepurified wash and rinse wastewaters; (i) biologically treating the prepurified wash and rinse wastewater by introducing it into a fixed-bed reactor containing activated sludge to form a mixture of treated wastewater and sludge; (j) separating the treated wastewater from the sludge; and (k) recirculating the treated wastewater back into the aqueous detergent-containing liquor, the rinse water, or both.

BACKGROUND OF THE INVENTION

This invention relates to a process for cleaning soiled materials, thewastewaters from the process being chemically, mechanically andbiologically treated and then returned to the process.

The industrial cleaning of soiled materials is normally carried out inwashing machines using a detergent-containing aqueous liquor. After theactual washing process, the washed material is repeatedly rinsed withwater and then dried and further processed. In this process, thedisposal of the wastewater accumulating, which is polluted withdetergent residues and other ingredients, represents a considerable costfactor. In the washing of feather or downs or in the washing of raw hidefor leather manufacture, the wastewater is polluted, for example, withlarge amounts of emulsified fat. In the washing of dyed cotton fabrics,for example in mechanical stone-wash washing with pumice stones or inthe washing of blue jeans, the wastewater contains dissolved and/ordispersed dyes and fiber residues.

In view of stricter anti-pollution legislation, the untreated wastewateris no longer allowed to leave the process so that treatment of thewastewater is unavoidable. The high consumption of freshwater for thetreatment process, especially in countries and regions with limitedwater resources, is also a considerable cost factor.

Accordingly, there is a need for a cleaning process for soiled materialswhich would involve minimal water consumption and hence could beoperated less expensively than known processes and which, at the sametime, would lead to reduced environmental pollution by wastewater.

SUMMARY OF THE INVENTION

The present invention therefore relates to a washing process for soiledmaterials in which the material to be washed is contacted with anaqueous detergent-containing liquor and then rinsed at least once withwater, the wastewater from the wash and rinse cycles is collected,chemically, mechanically and biologically treated and then returned tothe washing process, characterized in that the treated wastewater isused both for the rinse cycle and, after addition of the detergent, forthe wash cycle.

The process according to the invention is particularly suitable forwashing fat-soiled material, the wastewater being treated by

A) complete or partial treatment in a fat separator after addition of ademulsifier and then

B) mechanical prepurification by flotation and/or sedimentation beforethe biological treatment step.

In the context of the invention, fat-soiled material is understood to bematerial which contains 0.3 to 16% by weight of fat, based on the weightof the material. The term “fat” in the context of the inventionencompasses natural or synthetic glycerol esters of higher fatty acidsas described, for example, in Römpps Chemie Lexikon, Vol. 2, pages1339-1342, 1990. The process according to the invention is particularlysuitable for cleaning feathers or downs. Besides fat, feathers and downscontain skin particles, blood, droppings, vegetable impurities and largequantities of dust. Fat-soiled material in the sense of the presentinvention also occurs in the washing of leather, especially raw hides.

However, the process according to the invention is also suitable forwashing dye-soiled material, i.e. in the context of the inventionmaterial which releases dyes into the wastewater during washing. In thiscase, the wastewater is treated by complete or partial chemical andmechanical prepurification by

a) reaction with a suitable oxidizing agent and then

b) flotation and/or sedimentation before the biological treatment step.

Materials which release dyes into the wastewater include, for example,freshly dyed cotton fabrics or other textiles where excess dye is to beremoved by washing as, for example, in mechanical stone-wash washingwith pumice stones or in the washing of blue jeans.

The soiled material is washed in a suitable washing machine, for examplea cylinder washing machine or a washer-extractor. Washing is normallycarried out at temperatures of 5° C. to 60° C. However, feathers arepreferably washed with cold water at temperatures of 20° C. to 30° C.while blue jeans are normally washed at up 60° C.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a flow chart showing the steps of the claimed process.

DETAILED DESCRIPTION OF THE INVENTION

Detergents suitable for cleaning the material include any of thebiodegradable types known to the expert for this purpose. Thesedetergents normally contain anionic, cationic and/or nonionicsurfactants. It is of particular advantage to use detergents based onnonionic surfactants, for example C₇₋₁₅ fatty alcohols which have beenreacted with 3 to 10 mol of ethylene and/or propylene oxide per mol offatty alcohol. Other suitable detergent ingredients are diethyleneglycol ethers, more particularly diethylene glycol monobutyl ether, andreaction products of ethylene and/or propylene oxide with fatty acids.Reaction products of C₁₀₋₂₀ fatty acids with 8 to 12 mol of ethyleneoxide per molecule of fatty acid are particularly suitable.

The quantity of detergent used depends mainly on the degree of soilingof the material. The detergent is preferably used in quantities of 0.1to 5% by weight, based on the weight of the material to be washed. Inaddition, the process according to the invention is designed in such away that the quantity ratio of material to water is preferably between1:5 and 1:15. Besides the detergents described above, other substancesmay be used in the process according to the invention in the washing andrinsing steps, including for example antistatic agents, odor inhibitors,bleaching agents, water softeners, blueing agents and bacteriostaticagents. These auxiliaries are added to the wash or rinse liquor in thequantities known to the expert, normally between 0.1 and 3% by weight,based on the weight of the material to be washed.

The process according to the invention is distinguished by the fact thatthe water used in the washing and rinsing steps contains treatedwastewater which has been returned to the process. The consumption offreshwater and hence the washing costs are thus reduced. The water usedin the process preferably contains up to 80% by weight of treatedwastewater. However, the process may also be designed with advantage insuch a way that the proportion of freshwater that has to be added to thecircuit can be reduced to 10% by weight. The wastewater can thus bealmost completely recovered. The water losses are mainly attributable toevaporation and to the removal of water in the moisture of the washedmaterial after undergoing the washing process.

After the washing step, the washing water is pumped off and the materialis rinsed with water. Detergent residues and fat or dyes and optionallysolids adhering to the washed material are rinsed off in the rinsingstep until the rinsing water is clear. This may be done in the washingmachine itself or in a separate rinsing unit. The rinsing steps arepreferably carried out in the washing machine.

The quantity ratio of washed material to rinsing water is preferablybetween 1:5 and 1:40 per rinse cycle. The washed material is rinsed withwater at least once but preferably several times, more particularlybetween 3 and 6 times.

The washing process according to the invention is advantageouslydesigned in such a way that between 3 and 6 cubic meters of water arerequired for the complete washing of 100 kg of material, i.e. for thewashing and rinsing steps.

The wastewaters from the rinse cycles are also collected, combined withthe wastewater of the washing step, chemically, mechanically and thenbiologically treated and returned to the process. To this end, thewastewaters from the washing and rinsing steps are first completely orpartly prepurified both chemically and mechanically.

In the case of fat-containing soils, a suitable chemical which breaks upthe fat/water emulsion is first added to the wastewater. Iron salts,such as FeCl₃, are preferably used as demulsifiers, although AlCl₃ ormixtures with iron salts may also be used. The demulsifier is used inquantities of preferably 1 to 10 g/m³ wastewater and more preferably 2to 5 g/m³ wastewater.

The chemically treated wastewater is then introduced into a fatseparator. Any units and equipment known to the expert may be used forthis purpose. The fat globules separated off float on the surface of thewater and are mechanically removed.

The wastewater thus prepurified is then freed from any solids present byflotation and/or sedimentation. It is preferably subjected both tosedimentation to remove coarse solids and to flotation to removefine-particle soil, for example feather dust. This step may also becarried out in flotation or sedimentation units known to the expert.

If materials which release dyes to the wastewater are washed, thechemical treatment is carried out by first adding to the wastewater asuitable oxidizing agent which reacts with the dyes dissolved ordispersed in the water. Ozone is preferably used as this oxidizing agentin the process according to the invention.

The chemically and mechanically pretreated wastewater is thentransferred to a biological treatment stage in which the wastewater isfree from the surfactant residues. The biological treatment stagenormally consists of a fixed-bed reactor and activated sludge. Adegradation of more than 95% by weight of the surfactants is normallyachieved in such treatment units. The treated wastewater is thenintroduced into a secondary sedimentation tank to separate the sludgefrom the water. The sludge accumulating there is dewatered and may thenbe put to use, for example as an agricultural fertilizer.

The wastewater thus treated may now be reused for the wash and rinsecycles. However, it has proved to be of advantage further to treat thewastewater—after the biological stage—in an aftertreatment step carriedout by flocculation in the presence of a flocculation aid. Bacterialmass or activated sludge discharged from the biological treatment stageis removed by this aftertreatment. The flocculation agent used in thisaftertreatment may be selected from any of the compounds known to theexpert for this purpose, anionically modified polyacrylamides preferablybeing used. To this end, the flocculating agent is used in quantities of0.1 to 2 g/m³ wastewater and preferably in quantities of 0.5 to 1 g/m³wastewater. However, it can also be of advantage to filter thewastewater following the aftertreatment before it is returned to thewash and rinse cycles. This filtered water is particularly suitable forthe final rinse cycle of the process.

In a particularly preferred embodiment of the process according to theinvention, only the wastewater of the wash cycle and the first rinsecycle is chemically pretrated and the used water of the other rinsecycles is collected in an equalization tank. The chemically pretreatedwastewater is combined with the water from the equalization tank and thecombined wastewaters are then further prepurified by flotation and/orsedimentation and subsequently delivered to the biological treatmentstage.

It can also be of advantage to design the process in such a way that thewastewater of the washing step is treated and the wastewater thustreated is used in countercurrent in the rinsing units. The wastewaterfrom the rinsing units is then used for washing after addition of thedetergents and other auxiliaries required and subsequently resubjectedto the treatment process.

The process according to the invention enables soiled materials to beinexpensively washed. The materials are generally washed in batches. Thewastewater accumulating is treated, being circulated—preferablycontinuously—to this end. However, to ensure that the biologicaltreatment stage retains its cleaning effect, nutrient-containing waterhas to be continuously passed through this treatment stage. Accordingly,the problem arises of designing the process in such a way that, evenwhere the level of pollution by waste matter is low and innon-operational periods, the biological treatment stage retains itscleaning effect because the bacterial lawn and/or the activated sludgewould soon lose activity without sufficient nutrients from thewastewater. Accordingly, it has proved to be of advantage to design theprocess in these periods in such a way that the water is circulatedbetween the equalization tank and the biological treatment stage. Inorder to retain the activity of the bacterial lawn or the bacterialflocs, a suitable food for bacteria is added in sufficient quantities tothe water. This food provides the bacteria with the missing nutrients,particularly nitrogen and phosphorus.

EXAMPLE

The washing of feathers is described in the following as an example ofthe washing process according to the invention.

FIG. 1 is a flow chart of the process.

The following quantities of water were used to wash 100 kg of feathers:

1000 l of water in the washing step

1000 l of water in the 1st rinse

500 l of water in the 2nd rinse

500 l of water in the 3rd rinse

500 l of water in the 4th rinse

1000 l of water in the 5th rinse.

The wash and rinse cycles were carried out in a washing machine. Theratio of washing water to feathers was 1:10. The feathers were soiledwith solids (feather dust etc.) and about 6.5% fat. About 0.5 to 1% fatremained on the feathers after washing so that ca. 5.5 to 6.0 g of fatentered 1 l of wash liquor. If the fat is assumed to be based on stearicacid, 1 g of fat corresponds to ca. 750 mg org. C and 6 g of fat to ca.4500 mg org. C. The wash liquor contained 3 kg of detergent and 0.5 kgof auxiliaries per 100 kg of feathers. The detergent contained 70% oforganic material of which about two thirds are org. C: accordingly, 3 gof detergent contain 1400 mg org. C. The auxiliary contains 50% organicmaterial of which about two thirds are org. C; accordingly, 0.5 g ofauxiliary contains 200 mg org. C.

1 l of wash liquor contains 4500 mg org. C from fat, 1400 mg of org. Cfrom the detergent and 200 mg org. C from the auxiliary, making a totalof 6100 mg org. C.

<3 g/l fat, <1 g/l detergent ingredients, ≦0.2 g/l auxiliary ingredientsand various quantities of solids were removed from the wash liquor andrinsing water of rinse 1. They were introduced into the fat separatorafter demulsification with a demulsifier based on metal salt (MicroflocEFW, a product of Henkel KGaA). After fat separation, the wastewaterstill contained <1 mg/l fat. The other water ingredients were 20-30%removed, leaving 800 mg/l detergents ingredients, 150 mg/l auxiliaryingredients and various quantities of solids.

The following maximum quantities of org. C remained in 1 l pretreatedwastewater: 0.7 mg from fat, 500 mg from detergent and 100 mg fromauxiliary, making a total of 600 mg.

The pretreated wastewater (from the wash cycle and rinse 1) and thewastewater of the other rinses were combined in an equalization tank andthen subjected to flotation/sedimentation. The combination of the twowastewaters changed the contents of the wastewater as follows:

Substance [mg/l] Org. C [mg/l] Fat 0.5 0.3 Detergent 350 225 Auxiliary70 45 Total 270

The wastewater with these ingredients was freed from the solids in theflotation/sedimentation stage. This wastewater was introduced into animmersion-type bacteria bed reactor for biological treatment. Thisreactor consists of a fixed-bed reactor (wheels with upgrowth) andactivated sludge. Given a holding time of about 12 h, the biologicaldegradation can assumed to be >>95%.

After the biological treatment, the following C contents were obtainedper liter of wastewater: 0.3 mg from fat, 45 mg from detergent and 9 mgfrom auxiliary, making a total of <55 mg.

The treated wastewater from the activated-sludge stage was introducedinto a secondary sedimentation tank to separate the sludge from thewater. Flocculation/precipitation in the presence of a flocculant basedon an anionically modified polyacrylamide was then carried out forfurther purification. The water thus reconditioned was directly used forthe wash cycle and for rinses 1 to 4. The remaining water was filteredfor further purification and desalting. It was then used for the 5thrinse cycle. The water loss occurring was made up with freshwater (ca.10%) in the 5th rinse.

What is claimed is:
 1. A process for washing fat- or dye-soiledmaterials comprising: (a) providing a fat- or dye-soiled material; (b)providing an aqueous detergent-containing liquor; (c) contacting thefat- or dyesoiled material with the aqueous detergent-containing liquor,thus forming a washed material and wash wastewater; (d) providing asource of rinse water; (e) rinsing the washed material with the rinsewater, at least once, thus forming rinsed material and rinse wastewater;(f) collecting both the wash and rinse wastewater; (g) chemicallypretreating the collected wash and rinse wastewater by contacting itwith a compound selected from the group consisting of a demulsifier, anoxidizing agent and mixtures thereof, to form chemically pretreated washand rinse wastewater containing waste particles dispersed therein; (h)mechanically removing the waste particles from the chemically pretreatedwash and rinse wastewater by flotation or sedimentation to formprepurified wash and rinse wastewaters; (i) biologically treating theprepurified wash and rinse wastewater by introducing it into a fixed-bedreactor containing activated sludge to form a mixture of treatedwastewater and sludge; (j) separating the treated wastewater from thesludge; and (k) recirculating the treated wastewater back into theaqueous detergent containing liquor, the rinse water, or both.
 2. Theprocess of claim 1 wherein the fat- or dye-soiled material is afat-soiled material.
 3. The process of claim 2 wherein the compound of(g) is a demulsifier.
 4. The process of claim 3 wherein the demulsifieris selected from the group consisting of an iron salt, an aluminum saltand mixtures thereof.
 5. The process of claim 3 wherein the demulsifieris used in an amount of from 1 to 10 g/m³ of wastewater.
 6. The processof claim 1 wherein the fat- or dye-soiled material is a dye-soiledmaterial.
 7. The process of claim 6 wherein the compound of (g) is anoxidizing agent.
 8. The process of claim 7 wherein the oxidizing agentis ozone.
 9. The process of claim 1 wherein the aqueousdetergent-containing liquor of (b) and rinse water of (d) contain atleast 80% by weight of treated wastewater from (k).
 10. The process ofclaim 1 wherein the aqueous detergent-containing liquor contain from 1to 5% by weight of detergent, based on the weight of the fat- ordye-soiled material.
 11. The process of claim 1 further comprisingafter-treating the treated wastewater of (j), prior to recirculating it,by flocculation using a flocculation aid.
 12. The process of claim 11wherein the flocculation aid is an anionically modified polyacrylamide.13. The process of claim 11 wherein the flocculation aid is employed ina quantity of from 0.1 to 2 g/m³ of wastewater.
 14. The process of claim1 wherein the rinsed material of (e) is rinsed an additional 3 to 6times with the rinse water of (d), thus forming additional rinsewastewater.
 15. The process of claim 14 wherein the additional rinsewastewater is collected in an equalization tank and combined with thechemically pretreated wash and rinse wastewater of (g).